Basically, what is happening is that your user is either closing the browser tab, or is navigating away to a different page, before communication was complete. Your webserver (Jetty) generates this exception because it is unable to send the remaining bytes.
org.eclipse.jetty.io.EofException: null
! at org.eclipse.jetty.http.HttpGenerator.flushBuffer(HttpGenerator.java:914)
! at org.eclipse.jetty.http.HttpGenerator.complete(HttpGenerator.java:798)
! at org.eclipse.jetty.server.AbstractHttpConnection.completeResponse(AbstractHttpConnection.java:642)
!
This is not an error on your application logic side. This is simply due to user behavior. There is nothing wrong in your code per se.
There are two things you may be able to do: